Method for producing silica / alumina sol, silica / alumina sol, transparent film-forming coating material containing the sol, and substrate with transparent film

摘要

Disclosed are: a silica-alumina sol which is stable even when the sol is used at a high concentration and has good dispersibility in a matrix component; and a process for producing the sol. Silica-alumina particles are prepared by removing any cation (an alkali metal ion) that is derived from a production raw material from a silica-alumina sol, reducing the amount of any contaminant ion contained in the silica-alumina sol, and adjusting the amount of a negative charge present on the surface of the silica-alumina sol to a value falling within a predetermined range. The silica-alumina particles are used. An organosilicon compound is adsorbed on the surfaces of the particles in advance, and the compound is hydrolyzed, thereby treating the surfaces of the particles.